Such types of double tube joints are disclosed in Jikkai Sho-51 No. 161619 (Unexamined Japanese utility model publication No. 161619/1976) and Jikkai Hei-5 No. 30687 (Unexamined Japanese utility model publication No. 30687/1994).
In those known joints, the outer flow passages are connected mutually by jointing a male outer shell to the female outer shell so as to push movable valve elements arranged on tubular barrier walls backward. Further, the inner flow passages are connected mutually by abutting valve rods which are urged forward in the tubular barrier walls so as to push mutually rearward. Therefore, at a step when the male and female outer shells are connected mutually, though the movable valve element in the outer passage side becomes in contact with the outer shell, the valve rods should be in a state where the rods do not yet push mutually, since a space for enabling the valve rods to be projected is required at the abutting portion. In the state where a union nut is screwed, the movable valve elements go back to connect the outer passages mutually. However, air in the space between the ends of rods in the inner passages cannot escape out. Then, the valve rods go back and the inner passages are connected through with enclosing the air in the inner passages.
Therefore, when the double tube joint is used for the above-mentioned air-conditioner, hydraulic oil pipes or fuel feeding pipes, the air is undesirably entered and mixed in the fluid in the pipes at the step that the inner passages are connected mutually. Especially, in the case of a joint used in a refrigerant cycle pipes for a separate-type air-conditioner, moisture in the air is frozen and the system becomes unserviceable.